Etching method

ABSTRACT

A method for etching an insulation film through a patterned mask, includes the steps of etching the insulation film until just before an underlayer is about to be exposed by applying a plasma, and modifying a quality of a remaining film of the insulation film by applying another plasma which is different from the plasma used in the above etching process. The method further includes the process of removing the modified remaining film of the insulation film with a liquid chemical. The process of removing the modified remaining film can be also achieved by a dry etching method not employing a plasma.

FIELD OF THE INVENTION

The present invention relates to an etching method for forming anopening such as a contact hole or the like on an insulation film, and,more particularly, to an etching method capable of etching an insulationfilm exclusively without damaging an underlayer of a wafer.

BACKGROUND OF THE INVENTION

In order to form a hole as a contact hole on an insulation film or thelike, a plasma processing apparatus performs a dry etching such as ahigh anisotropic reactive ion etching or the like. FIG. 6 shows a caseof etching an object to be processed, e.g., a wafer in which aninsulation film 202, a hard mask 203 formed of SiO₂ or the like, ananti-reflection coating 204 and a resist film 205 are laminated on anunderlayer 201 in order.

First of all, as depicted in FIG. 6A, an opening 205A is formed in theresist film 205 by employing a photolithography process. Next, asillustrated in FIG. 6B, a dry etching is performed on theanti-reflection coating 204, the hard mask 205 and the insulation film202 by using the resist film 205 as a mask until the underlayer 201 isexposed, thereby forming an opening 206. During the dry etching, theunderlayer 201 as well as a sidewall of the opening 206 is irradiated byreactive ions or the like. Accordingly, the underlayer 201 is damaged asdepicted in FIG. 6B and, further, the damage inflicted on the underlayer201 hinders a wiring process or the like to be performed.

As described in FIG. 6C, a defective layer 206A has been removed througha conventional wet etching process. However, in case of the wet etchingprocess, since it is difficult to find out the exact thickness of thedefective layer 206A to be removed, it is very difficult to preciselyremove only the defective layer 206A and, thus, a surface of theunderlayer 201 tends to be overetched, thereby deteriorating afabrication accuracy. Therefore, there is suggested a technique forremoving the defective layer 206A while maintaining the fabricationaccuracy for forming the opening 206 to the utmost in Japanese PatentApplication Nos. H05-182871, H07-167680 and H08-144008 (hereinafter,referred to as Patent documents 1 to 3).

For example, the Patent document 1 suggests a semiconductor devicefabrication method involving forming an insulation film on an underlayerof a wafer, dry etching the insulation film by applying a patternedresist film as a mask, exposing the underlayer through an openinggenerated by dry etching, forming a selective oxide layer by oxidizing adefective layer formed on a surface of the underlayer during the dryetching process, and removing the selective oxide layer by a wetetching. In this method, while the defective layer formed on the surfaceof the underlayer is removed, an overetching onto the underlayer issuppressed by converting the defective layer into the selective oxidelayer by oxidizing it first before it is removed.

The Patent document 2 suggests a semiconductor device fabrication methodinvolving a first plasma etching process in which a part of aninter-layer insulation film is etched along a thickness directionthereof until a surface of a device area is about to be exposed and asecond plasma etching process in which a remaining part of theinter-layer insulation film in the thickness direction thereof is etchedby a gas capable of generating halogen-based chemical species other thanfluorine-based chemical species. In this method, the etching isperformed by using the gas capable of generating halogen-based chemicalspecies other than fluorine-based chemical species, thereby suppressingcarbon or fluorine contamination on the device area or a generation of adefective layer thereon.

The Patent document 3 suggests a semiconductor device fabrication methodinvolving dry etching an insulation film formed on a underlayer of awafer, and removing a defective layer formed on the surface of theunderlayer by irradiating accelerated oxygen ions thereon through anopening of the insulation film. In this method, since fluorine is notused for removing the defective layer, the surface of the underlayer isnot etched. As a result, irregularities are not generated on the surfaceof the underlayer.

In the conventional method of the Patent document 1, the insulation filmis dry etched until the silicon underlayer is exposed and the defectivelayer formed on the silicon underlayer is oxidized and converted into aselective oxide layer and, then, the selective oxide layer is wetetched. Accordingly, in case an underlayer or a device area is formed onthe surface of the silicon substrate, an etching selectivity of theinsulation film against the underlayer or the device region can be lowduring the dry etching process, and, further, the defective layer formedon the surface of the underlayer or the device area is removed by thewet etching. Therefore, it is possible to precisely and exclusively etchthe insulation film only, resulting in the erosion of the underlayer orthe device area.

Meanwhile, the underlayer keeps getting thinner along with a trend forhigh integration and high density of a semiconductor device. Forexample, a film thickness currently ranging from 50 nm to 100 nm isexpected to be reduced to range from 20 nm to 30 nm in a near future.Therefore, with the etching method of the Patent document 1, it is notpossible to cope with the trend for the thinner semiconductorunderlayer.

Further, in the conventional method of the Patent document 2, theetching is performed by using the gas capable of generatinghalogen-based chemical species other than fluorine-based chemicalspecies, thereby enabling to suppress carbon or fluorine contaminationon the device area or a generation of a defective layer thereon.However, it is not possible to completely prevent the contamination fromthe halogen-based chemical species (elements such as Cl, Br or the like)and the generation of the defective layer. Consequently, with theetching method of the Patent document 2, it is not possible to cope withthe trend for the thinner underlayer.

Furthermore, in the conventional method of the Patent document 3, sincethe defective layer formed on the surface of the underlayer is removedby irradiating accelerated oxygen ions thereon, energy of the oxygenions should be precisely controlled such that the surface of theunderlayer is not etched by the oxygen ions.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anetching method capable of etching an insulation film exclusively withhigh accuracy without damaging a semiconductor even while underlayerkeeps getting thinner along with the trend for high density and highintegration of a semiconductor device.

In accordance with a preferred embodiment of the present invention,there is provided a method for etching an insulation film through apatterned mask, the method includes,

a first process of etching the insulation film until just before anunderlayer is about to be exposed by applying a first plasma of a firstprocessing gas;

a second process of modifying a quality of a remaining film of theinsulation film by applying a second plasma of a second processing gas,the second plasma being different from the first plasma; and

a third process of removing the insulation film having a modified filmquality with a liquid chemical.

In accordance with another preferred embodiment of the presentinvention, there is provided a method for etching an insulation filmthrough a patterned mask, the method includes,

a first process of etching the insulation film until just before anunderlayer is about to be exposed by applying a first plasma of a firstprocessing gas;

a second process of modifying a quality of a remaining film of theinsulation film by applying a second plasma of a second processing gas,the second plasma being different from the first plasma; and

a third process of removing the insulation film having a modified filmquality through a dry etching process using no plasma.

Preferably, the insulation film is a SiCOH-based low dielectric constantinsulation film.

Preferably, the mask is a hard mask.

Preferably, the first processing gas is fluorocarbon gas.

Preferably, in the second process, a methyl group is mainly removed fromthe SiCOH-based low dielectric constant insulation film.

Preferably, the second processing gas contains at least H₂ gas or O₂gas.

Preferably, the liquid chemical contains at least one of hydrofluoricacid, ammonium fluoride and tetramethyl ammonium hydroxide.

Preferably, the dry etching process using no plasma employs a chemicaloxide removal method.

Preferably, the underlayer is formed of SiC or SiCN.

In accordance with still another preferred embodiment of the presentinvention, there is provided a method for etching a SiCOH-based lowdielectric constant insulation film, the method includes, a firstprocess of etching the SiCOH-based low dielectric constant insulationfilm with a fluorocarbon gas plasma without exposing an underlayer suchthat a thickness of a remaining SiCOH-based low dielectric constantinsulation film is smaller than or equal to 100 nm;

a second process of removing a methyl group from the remainingSiCOH-based low dielectric constant insulation film by applying a plasmacontaining H₂ gas or O₂ gas; and

a third process of removing the remaining SiCOH-based low dielectricconstant insulation film devoid of the methyl group with a solutioncontaining at least one of hydrofluoric acid, ammonium fluoride andtetramethyl ammonium hydroxide.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of preferred embodiments,given in conjunction with the accompanying drawings, in which:

FIG. 1 shows an exemplary plasma processing apparatus used for anetching method of the present invention;

FIG. 2 describes a cross sectional view of an exemplary liquid chemicalprocessor used for removing a remaining film of an etched low-k film;

FIGS. 3A and 3B provide cross sectional views of principal parts of awafer, which illustrate processes for etching the low-k film with theplasma processing apparatus of FIG. 1;

FIGS. 4A to 4C present cross sectional views of the principal parts ofthe wafer, which respectively depict a process for etching the low-kfilm with the plasma processing apparatus of FIG. 1, a process formodifying a quality of the remaining film of the low-k film, and aprocess for removing a defective layer with the liquid chemicalprocessor shown in FIG. 2 after the modification;

FIGS. 5A and 5B offer cross sectional views of an exemplary processingapparatus other than the liquid chemical processor used for removing themodified remaining film of the low-k film illustrated in FIG. 4C; and

FIGS. 6A to 6C represent sectional views of principal parts of a wafer,which show processes for etching a low-k film with a conventionaletching method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to FIGS. 1 to 5.

In an etching method of the present invention, an insulation film 102formed on an object (e.g., a wafer) is etched to form an opening 106 byusing a plasma processing apparatus 1 (see, FIG. 1) until an underlayer101 thereof is about to be exposed, that is, until a part of theinsulation film 102 still remains to be left. Thereafter, a quality of aremaining film 102A of the insulation film 102 is modified by using thesame plasma processing apparatus 1.

Next, the modified remaining film 102A of the insulation film 102 issubjected to a liquid chemical process using a liquid chemical processor20 (see, FIG. 2), so that the remaining film 102A of the insulation film102 can be precisely and exclusively removed without damaging theunderlayer 101. Hereinafter, the plasma processing apparatus 1 and theliquid chemical processor 20 will be explained and, then, a firstpreferred embodiment of the etching method of the present invention willbe described.

The plasma processing apparatus 1 used for the etching method of thepresent invention includes an electrically grounded processing chamber 2having an alumite processed surface, which can be maintained at adesired high vacuum level; a lower electrode 3 disposed at a centralportion of a bottom surface of the processing chamber 2, for mountingthereon a wafer W; a support 4 provided on an insulation plate 2A on thebottom surface of the processing chamber 2, for supporting the lowerelectrode 3 from below; and a hollow upper electrode 5 spaced apart fromthe lower electrode 3. Such plasma processing apparatus 1 is configuredto etch an insulation film of the wafer until an underlayer is about tobe exposed and then modify a remaining film of the etched insulationfilm.

A first high frequency power supply 6 of, e.g., 2 MHz, is connected tothe lower electrode 3 via a matching unit 6A, whereas a second highfrequency power supply 7 having a frequency, e.g., 60 MHz, higher thanthat applied to the lower electrode 3 is connected to the upperelectrode 5 via a matching unit 7A. Further, a high pass filter 8 isconnected to the lower electrode 3, whereas a low pass filter 9 isconnected to the upper electrode 5. Moreover, a gas evacuation unit 11is connected to an evacuation port 2B provided on the bottom surface ofthe processing chamber 2 via an gas line 11A and maintains theprocessing chamber 2 at a desired vacuum level by vacuum exhausting theprocessing chamber 2. Hereinafter, if necessary, the lower electrode 3and the support 4 will be referred together as a mounting table 10.

A gas supply line 5A is formed at a central portion of a top surface ofthe upper electrode 5 and is inserted into a central portion of a topsurface of the processing chamber 2 via the insulation member 2C.Further, a gas source 12 is connected to the gas supply line 5A via agas supply line 13 and supplies an etching gas. To be specific, the gassource 12 includes a first gas (e.g., C₄F₈) source 12A, a second gas(e.g., Ar) source 12B, a third gas (e.g., N₂) source 12C, a fourth gas(e.g., O₂) source 12D, a fifth gas (e.g., H₂) source 12E, and mass flowcontrollers (12F, 12G, 12H, 121 and 12J) of the respective gas sources12A to 12E, wherein the gas sources 12A to 12E are connected to the gassupply line 13 via the mass flow controllers 12F to 12J, respectively.

Moreover, the gas source 12 combines gases from those gas sources 12A to12E and then supplies the gas mixture into a hollow portion inside theupper electrode 5 at a predetermined flow rate ratio. A plurality of gasinjection openings 5B are uniformly distributed on a bottom surface ofthe upper electrode 5. A plurality of gases introduced from the gassource 12 are mixed and then uniformly supplied as an etching gas or asurface modifying gas into the processing chamber 2 through the gasinjection openings 5B.

The processing chamber 2 is vacuum exhausted by the gas evacuation unit11, and a specific etching gas is supplied thereto from the gas source12 at a predetermined flow rate. In this state, by applying a highfrequency power to the lower and the upper electrode 3 and 5, a plasmaof the etching gas (or the surface modifying gas) is generated insidethe processing chamber 2 to be used in performing a specific etching orsurface modification on the wafer W on the lower electrode 3. Atemperature sensor (not shown) is attached to the lower electrode 3 tobe used to constantly monitor a temperature of the wafer W on the lowerelectrode 3.

Formed inside the mounting table 10 is an internal coolant channel 10Awhere a specific coolant (e.g., a conventionally well knownfluorine-based fluid, water or the like) passes through. The lowerelectrode 3 and the wafer W on the lower electrode 3 are cooled whilethe coolant is flowing in the internal coolant channel 10A, so that thewafer W is controlled to be maintained at a desired temperature.Further, an electrostatic chuck 14 made of an insulating material isdisposed on the lower electrode 3, and a high voltage DC power supply 15is connected to an electrode plate 14A inside the electrostatic chuck14. The electrostatic chuck 14 electrostatically adsorbs the wafer Wwith an electrostatic force generated on a surface by a high voltageapplied from the high voltage DC power supply 15 to the electrode plate14A. A focus ring 16 surrounding the electrostatic chuck 14 is disposedat an outer periphery of the lower electrode 3 to focus the plasma onthe wafer W.

Moreover, formed at the mounting table 10 is a gas channel 10B forsupplying a thermally conductive gas such as He gas or the like as abackside gas. The gas channel 10B has openings at multiple locations ona top surface of the mounting table 10. Those openings match withthrough holes formed at the electrostatic chuck 14 on the mounting table10.

Thus, if the backside gas is supplied to the gas channel 10B of themounting table 10, the backside gas is discharged through the throughholes of the electrostatic chuck 14 via the gas channel 10B to beuniformly diffused into an entire gap between the electrostatic chuck 14and the wafer W to thereby increase a thermal conductivity in the gap.Further, referring to FIG. 1, there is illustrated a gate valve 17formed at the processing chamber 2, for allowing the wafer W to becarried into or out of the processing chamber 2.

In the aforementioned plasma processing apparatus 1, the opening 106 isformed on the insulation film 102 by performing the etching process onthe wafer W and, then, the quality of the remaining film 102A generatedduring the etching process in the insulation film 102 is modified.Thereafter, the modified remaining film 102A of the insulation film 102is removed by a liquid chemical processor 20 to be described later.Accordingly, an etching selectivity of the remaining film 102A againstthe underlayer 101 becomes infinite. As a result, the remaining film102A can be exclusively removed without damaging the underlayer 101.

As shown in FIG. 2, for example, the liquid chemical processor 20includes a wafer chuck 21 that can be moved up and down, a motor 22 forrotating the wafer chuck 21, a liquid chemical supply unit 23 arrangedto be separated from the motor 22, for supplying a liquid chemical to acentral portion of a top surface of the wafer W electrostaticallyadsorbed to be held by the wafer chuck 21, and a ring-shaped receptacle24 for collecting the liquid chemical dispersed from the surface of thewafer W after the processing. Those components are supported by asupport plate 25.

Still referring to FIG. 2, the wafer chuck 21 is lifted up and down by aelevating mechanism 26 surrounding an upper portion of the motor 22. Theliquid chemical supply unit 23 includes a liquid chemical supply line23A connected to a liquid chemical tank (not shown), a nozzle 23Battached to a leading end of the liquid chemical supply line 23A, asupporting arm 23C for supporting the nozzle 23B and a driving body 23Dfor elevating the supporting arm 23C, wherein the nozzle 23B supplies aliquid chemical to a central portion of the wafer W held by the waferchuck 21. The liquid chemical supply unit 23 is also used for supplyinga cleaning fluid such as pure water or the like. In case the wafer W iscleaned, a cleaning brush 27 disposed above the wafer chuck 21 is used.

Moreover, the ring-shaped receptacle 24 is formed in an approximatedoughnut shape, and an opening 24A is formed along an upper portion ofan inner peripheral surface, thereby collecting liquid chemicaldispersed from the rotating wafer W through the opening 24A after theprocessing. Further, an exhaust line 24B is formed on a bottom surfaceof the ring-shaped receptacle 24 which passes through the support plate25 downwardly, thereby discharging the liquid chemical into apredetermined collection tank (not shown) through the exhaust line 24Bafter the processing.

Hereinafter, a first preferred embodiment of the etching method of thepresent invention using the plasma processing apparatus 1 and the liquidchemical processor 20 will be described with reference to FIGS. 3 and 4.In this embodiment, as shown in FIGS. 3A and 3B, an etching process isperformed on the wafer W in which an underlayer 101, a SiCOH-based lowdielectric constant insulation film (hereinafter, referred to as ‘low-kfilm’) 102, a hard mask 103, an anti-reflection coating 104 and a resistfilm 105 are laminated in order. The underlayer 101 is formed of, e.g.,SiC, SiCN or the like. The SiCOH-based low-k film 102 is made of anorganic material including Si, C, O and H, e.g., amethyl-hydrogen-silsesquioxane (MSQ)-based organic material or the like.Further, the hard mask 103 is formed of, e.g., SiO₂, SiN_(x) or thelike. Moreover, an opening 105A is formed in advance in the resist film105 in a specific pattern by a photolithography process.

Once the aforementioned wafer W is supplied to the plasma processingapparatus 1, the gate valve 17 of the plasma processing apparatus 1 isopened and, then, the wafer W is loaded into the processing chamber 2through the loading/unloading port. When the wafer W is mounted on thelower electrode 3, the wafer W is fixed on the electrostatic chuck 14 bythe electrostatic adsorption. After the loading/unloading port is closedby closing the gate valve 17, the first to the third gas source 12A to12C of the gas source 12 respectively supply C₄F₈ gas, Ar gas and N₂ gasas etching gases at a predetermined flow rate ratio toward a top surfaceof the wafer W through the gas injection openings 5B of the upperelectrode 5.

At this time, the respective gas flow rates of C₄F₈ gas, Ar gas and N₂gas preferably range from 4 sccm to 6 sccm, from 500 sccm to 1000 sccm,and from 100 sccm to 200 sccm, for example. Further, a gas pressureinside the processing chamber 2 preferably ranges from 50 mTorr to 75mTorr, for example. During the etching process, He gas is supplied to abackside of the wafer W at a controlled flow rate, thereby cooling thewafer W.

If the inner space of the processing chamber 2 is stabilized to bemaintained at a predetermined vacuum level, high frequency powers areapplied from the first high frequency power supply 6 and the second highfrequency power supply 7, respectively, thereby generating a plasma ofthe etching gases between the lower electrode 3 and the upper electrode5. The high frequency power applied from the first high frequency powersupply 6 preferably ranges from 400 W to 1700 W, for example. Moreover,the high frequency power applied from the second high frequency powersupply 7 preferably ranges from 300 W to 1200 W, for example.

If an anisotropic etching is performed on the wafer W shown in FIG. 3Aby using the resist film 105 as a mask under the aforementionedconditions, the anti-reflection coating 104, the hard mask 103 and thelow-k film 102 are etched, thereby forming the opening 106 asillustrated in FIG. 3B. In this embodiment, the supply of C₄F₈ gas, Argas, and N₂ gas is suspended right before the underlayer 101 is about tobe exposed and, then, the etching process is stopped. Accordingly, asshown in FIG. 3B, a part of the low-k film 102 remains to be left as theremaining film 102A on the underlayer 101. A film thickness of theremaining film 102A is preferably smaller than or equal to 100 nm, and,more preferably, it ranges from 30 nm to 50 nm. If it is smaller than 30nm, a defective layer may be formed on the underlayer 101. On thecontrary, if it is greater than 100 nm, the remaining film 102A may notbe completely removed by an after-treatment followed by the etchingprocess. Herein, the film thickness of the remaining film 102A can bemanaged by controlling, e.g., an etching time or the like.

When forming the opening 106 by etching the Low-K film 102, there aregenerally formed a defective layer 106A on the bottom surface and thesidewall surface of the opening 106.

However, in this embodiment, since the remaining film 102A is left abovethe underlayer 101, a defective layer is not formed on a surface of theunderlayer 101. Instead, the defective layer 106A is formed on a surfaceof the remaining film 102A and on the sidewall surface of the opening106. Accordingly, the defective layer 106A remains to be left inside theopening 106, it needs to be removed.

Accordingly, in this embodiment, after the etching process, a qualitymodification process is performed on the remaining film 102A of thelow-k film 102 in the same plasma processing apparatus 1.

To be specific, the first to third gas sources 12A to 12C of the gassource 12 are switched off and instead, O₂ gas is supplied as amodifying gas at a specific flow rate from the fourth gas source 12Dinto the processing chamber 2. At this time, a flow rate of O₂ gaspreferably ranges from 100 sccm to 300 sccm, for example. Further, thegas pressure inside the processing chamber 2 preferably ranges from 5mTorr to 20 mTorr, for example. A high frequency power applied from thefirst high frequency power supply 6 preferably ranges from 100 W to 300W, for example, whereas that applied from the second high frequencypower supply 7 preferably ranges from 0 W to 300 W, for example. Otherconditions remain to be same as those of the etching process.

If a plasma is generated from O₂ gas under the aforementioned conditionsand, then, the oxygen plasma is applied onto the wafer W illustrated inFIG. 4A, a methyl group forming the remaining film 102A of the low-kfilm 102 reacts to oxygen and then is removed by the oxidation.Consequently, as depicted in FIG. 4B, the remaining film 102A of thelow-k film 102 is modified into glass components SiO_(x) including Siand O. After the quality modification process is completed, a liquidchemical processing is performed on the wafer W to thereby remove themodified portion of the wafer W.

Further, instead of oxygen gas, a gas mixture of N₂ and H₂ can be usedas the modifying gas in modifying the remaining film 102A of the low-kfilm 102. In this case, a flow rate of N₂ gas preferably ranges from 0sccm to 200 sccm, and that of H₂ gas preferably ranges from 200 sccm to0 sccm, for example. Furthermore, the gas pressure inside the processingchamber 2 preferably ranges from 10 mTorr to 50 mTorr, for example. Eachof high frequency powers applied from the first and the second highfrequency power supply 6 and 7 preferably ranges from 100 W to 500 W,for example. Other conditions remain to be same as those of the etchingprocess. Besides, before the quality modification process, the resistfilm 105 on the surface of the wafer W is removed by an ashing using anashing apparatus (not shown).

Hereinafter, a method for removing the modified remaining film 102A ofthe low-k film 102 with the liquid chemical processor 20 will bedescribed. In this embodiment, as for a liquid chemical, a solutioncontaining at least one of hydrofluoric acid, ammonium fluoride, andtetramethyl ammonium hydroxide is preferably used. Hereinafter, therewill be described a case of using a dilute hydrofluoric acid. Once thewafer W is supplied to the liquid chemical processor 20 by a transfermechanism (not shown), the wafer chuck 21 thereof is elevated by theelevating mechanism 26 and then receives the wafer W in the liquidchemical processor 20.

Next, the wafer chuck 21 holding the wafer W is driven to rotate by themotor 22 at a high speed. In this state, if the dilute hydrofluoric acidis supplied through the nozzle 23B of the liquid chemical supply unit 23to a top central surface of the wafer W, the dilute hydrofluoric acidreacts with the glass components of the remaining film 102A of the low-kfilm 102 and dissolve the glass components including mainly Si and O,resulting in a removal of the remaining film 102A of the low-k film 102.

At this time, a volume ratio between hydrofluoric acid and water in thedilute hydrofluoric acid used herein is 1:100, for example, and theprocessing is performed for 30 seconds to one minute. Since the dilutehydrofluoric acid does not react with SiC of the underlayer 101, theremaining film 102A is exclusively and completely removed withoutdamaging the underlayer 101. Further, the defective layer 106A generatedby the etching is also removed by the liquid chemical processing. Afterthe processing, the dilute hydrofluoric acid containing SiF₄ isdispersed from the surface of the wafer W to thereby be collected in thering-shaped receptacle 24 via the opening 24A. The collected liquid isdischarged from the ring-shaped receptacle 24 through the exhaust line24B of the ring-shaped receptacle 24.

As described above, this embodiment involves a first step of forming theopening 106 by etching the low-k film 102 until right before theunderlayer 101 is about to be exposed by applying a plasma of an etchinggas containing C₄F₈ through the resist film 105 having the opening 105Aformed in a specific pattern, a second step of modifying a quality ofthe remaining film 102A of the low-k film 102 by applying the plasma ofoxygen gas onto the remaining film 102A of the low-k film 102, and athird step of removing the modified remaining film 102A of the low-kfilm 102 with the dilute hydrofluoric acid.

Accordingly, the remaining film 102A of the low-k film 102 can beexclusively removed. Moreover, since the modified remaining film 102A ofthe low-k film 102 by the dilute hydrofluoric acid is removed by a wetetching process, a wet etching selectivity for the underlayer 101becomes infinite. Accordingly, the opening 106 can be formed with highaccuracy without damaging the surface of the underlayer 101. Therefore,even if the underlayer 101 and the low-k film 102 keeps getting thinneralong with the trend for high density and high integration of asemiconductor device, the low-k film 102 can be exclusively etchedwithout damaging the underlayer 101.

In this embodiment, there has been described a method for removing themodified remaining film 102A of the low-k film 102 through the wetetching by using a liquid chemical containing fluorine. However, as willbe described hereinafter, the modified remaining film 102A of the low-kfilm 102 can also be removed by using apparatuses for performing achemical oxide removal (COR) method illustrated in FIG. 5A (hereinafter,referred to as “COR apparatus”) and a post heat treatment shown in FIG.5B (hereinafter, referred to as “PHT apparatus”)

Specifically, as shown in FIG. 5A, a COR apparatus 30 includes a vacuumprocessing chamber 31, a mounting table 32 for the wafer W, disposed ata central portion of a bottom surface inside the processing chamber 31,and a shower head 33 provided at an upper ceiling of the processingchamber 31. The COR apparatus 30 performs a COR process for convertingthe modified remaining film 102A of the low-k film 102 of the wafer W onthe mounting table 32 into volatile chemical compounds by using aprocessing gas supplied through the shower head 33 into the processingchamber 31. The COR process is a dry etching process using no plasma. Tobe specific, the modified remaining film 102A of the low-k film 102 isconverted into volatile chemical compounds due to a chemical reactionwith a processing gas to be removed thereafter, wherein no plasma isgenerated from the processing gas.

As shown in FIG. 5A, an evacuation port 31A formed on a bottom surfaceof the processing chamber 31 is provided at an outer portion of themounting table 32. After the treatment, the gas is discharged to theoutside through the evacuation port 31A. An electrostatic chuck (notshown) is provided on a top surface of the mounting table 32, and acoolant channel 32A for circulating a coolant is formed therein.Further, a first gas supply line 33A and a second gas supply line 33Bare formed on a top surface of the shower head 33, and a plurality ofgas injection openings 33C are formed on a bottom surface of the showerhead 33, i.e., on an upper wall of the processing chamber 31.Accordingly, the shower head 33 supplies a processing gas introducedfrom the first and the second gas supply line 33A and 33B into theprocessing chamber 31 through the gas injection openings 33C.

As for the processing gas, a gas mixture of ammonia gas and hydrogenfluoride gas, for example, is preferably used as shown in FIG. 5A.Moreover, an Ar gas may be added thereto. Herein, it is preferable toset a flow rate of the ammonia gas to be greater than that of thehydrogen fluoride gas. For example, a flow rate (sccm) ratio of theammonia gas to the hydrogen fluoride gas is preferably in the range of1:1 to 2:1. Further, a pressure of the gas mixture inside the processingchamber 31 preferably ranges from 10 mTorr to 40 mTorr. A temperature ofthe mounting table 32 is preferably set to be kept at 25° C., forexample. As will be shown in a following chemical formula, by performingthe COR process in which the aforementioned gases react with the glasscomponents SiO₂ of the modified remaining film 102A of the low-k film102 of the wafer W, a volatile gas component and volatile complexcompound (NH₄)₂SiF₆. are generated.

[COR Process]SiO₂+4HF→SiF₄+2H₂O↑SiF₄+2NH₃+2HF→(NH₄)₂SiF₆

Meanwhile, as illustrated in FIG. 5B, a PHT apparatus 40 includes aprocessing chamber 41 and a mounting table 42 for accommodating thereina heater 42A and performs a PHT process by heating a wafer W that hasbeen subjected to the COR process. Accordingly, as depicted in thefollowing chemical formula of the PHT process, the volatile complexcompound is thermally decomposed into volatile gas components to becompletely volatilized and, then, removed from the wafer W. In addition,an evacuation port 41A formed on a bottom surface of the processingchamber 41 is provided at an outer portion of the mounting table 42. Thevolatilized gas compounds are discharged by supplying a predeterminedgas (e.g., unreactive gas such as nitrogen gas or the like) through ashower head (not shown).

The wafer W is preferably heated in the range of 80° C. to 200° C., forexample. Further, a processing time of the wafer W preferably rangesfrom 60 seconds to 180 seconds, and a gas pressure inside the processingchamber 41 preferably ranges from 500 mTorr to 1 Torr, for example. Aflow rate of the unreactive gas such as a nitrogen gas or the likepreferably ranges from 500 sccm to 3000 sccm, for example. Moreover, asshown in FIG. 5B, during the PHT process, N₂ and H₂ are slightlyvolatilized in addition to following volatile compounds.

[PHT process](NH₄)₂SiF₆→SiF₄↑+2NH₃↑+2NF↑

As described above, in accordance with this embodiment, the COR processand the PHT process are sequentially performed in removing the modifiedremaining film 102A of the low-k film 102. Accordingly, the modifiedremaining film 102A of the low-k film 102 is converted into the chemicalcompounds to be volatilized and, then completely removed. As a result, asurface of the underlayer 101 can be exposed without being damaged.

The present invention is not limited to the aforementioned embodiment.Although the aforementioned embodiment has described a case where thehard mask 103, the anti-reflection coating 104 and the resist film 105are laminated on the low-k film 102, the present invention can also beapplied to a case where the anti-reflection coating 104 and the resistfilm 105 are removed and, then, an etching is performed by using thehard mask 103 as a mask.

That is, the present invention includes the method of forming theopening 106 by etching the insulation film 102 until just before theunderlayer 102 is about to be exposed, modifying a quality of theremaining film 102A thereof on a bottom surface of the opening 106 byapplying a plasma of an additional gas other than the etching gas, andremoving the modified portion with a liquid chemical. In addition,instead of a wet etching method, the present invention includes a dryetching method using no plasma, e.g, the COR process, and then removinga modified remaining film 102A.

The present invention is suitable for an etching method for etching aninsulation film to form a opening.

In accordance with the present invention, there can be provided anetching method capable of etching an insulation film exclusively withhigh accuracy without damaging the underlayer even while the wafer keepsgetting thinner along with the trend for high density and highintegration of a semiconductor device.

While the invention has been shown and described with respect to thepreferred embodiments, it will be understood by those skilled in the artthat various changes and modification may be made without departing fromthe scope of the invention as defined in the following claims.

1. A method for etching an insulation film through a patterned mask,comprising: a first process of etching the insulation film until justbefore an underlayer is about to be exposed by applying a first plasmaof a first processing gas; a second process of modifying a quality of aremaining film of the insulation film by applying a second plasma of asecond processing gas, the second plasma being different from the firstplasma; and a third process of removing the insulation film having amodified film quality with a liquid chemical.
 2. A method for etching aninsulation film through a patterned mask, comprising: a first process ofetching the insulation film until just before an underlayer is about tobe exposed by applying a first plasma of a first processing gas; asecond process of modifying a quality of a remaining film of theinsulation film by applying a second plasma of a second processing gas,the second plasma being different from the first plasma; and a thirdprocess of removing the insulation film having a modified film qualitythrough a dry etching process using no plasma.
 3. The method of claim 1,wherein the insulation film is a SiCOH-based low dielectric constantinsulation film.
 4. The method of claim 2, wherein the insulation filmis a SiCOH-based low dielectric constant insulation film.
 5. The methodof claim 1, wherein the mask includes a hard mask.
 6. The method ofclaim 2, wherein the mask includes a hard mask.
 7. The method of claim1, wherein the first processing gas is fluorocarbon gas.
 8. The methodof claim 2, wherein the first processing gas is fluorocarbon gas.
 9. Themethod of claim 3, wherein in the second process; a methyl group ismainly removed from the SiCOH-based low dielectric constant insulationfilm.
 10. The method of claim 1, wherein the second processing gascontains at least H₂ gas or O₂ gas.
 11. The method of claim 2, whereinthe second processing gas contains at least H₂ gas or O₂ gas.
 12. Themethod of claim 1, wherein the liquid chemical contains at least one ofhydrofluoric acid, ammonium fluoride and tetramethyl ammonium hydroxide.13. The method of claim 2, wherein the dry etching process using noplasma employs a chemical oxide removal method.
 14. The method of claim1, wherein the underlayer is formed of SiC or SiCN.
 15. The method ofclaim 2, wherein the underlayer is formed of SiC or SiCN.
 16. A methodfor etching a SiCOH-based low dielectric constant insulation film,comprising: a first process of etching the SiCOH-based low dielectricconstant insulation film with a fluorocarbon gas plasma without exposingan underlayer such that a thickness of a remaining SiCOH-based lowdielectric constant insulation film is smaller than or equal to 100 nm;a second process of removing a methyl group from the remainingSiCOH-based low dielectric constant insulation film by applying a plasmacontaining H₂ gas or O₂ gas; and a third process of removing theremaining SiCOH-based low dielectric constant insulation film devoid ofthe methyl group with a solution containing at least one of hydrofluoricacid, ammonium fluoride and tetramethyl ammonium hydroxide.